Running a musical entertainment into chaos (9)
I believe the answer is:
operation
'running' is the definition.
(I've seen this before)
'a musical entertainment into chaos' is the wordplay.
'a musical entertainment' becomes 'opera' (I've seen this before).
'chaos' is an anagram indicator.
'into' anagrammed gives 'tion'.
'opera'+'tion'='OPERATION'
(Other definitions for operation that I've seen before include "military undertaking" , "Business" , "Procedure; enterprise" , "performance" , "Manoeuvre - military action" .)